1. Field of the Invention
This invention relates to a gear pump, and more particularly to a gear pump which is adapted to circulate low pressure oil on a suction side to lubricate and cool gear shafts of the gear pump.
2. Description of the Prior Art
A conventional gear pump is typically constructed in a manner as shown in FIGS. 1 to 3. More particularly, it includes a body section 1 and a pair of gears 2 and 3 arranged in the body section 1. The body section 1 is closed on both sides thereof with a cover 4 and a mounting flange 5. The mounting flange 5 and cover 4 are each formed with a pair of bushing insertion holes 6, 7 and 8, 9 into which each pair of bearing bushings 10, 11 and 12, 13 is securely inserted to support each pair of gear shafts 14, 15 and 16, 17 therein, respectively. On both sides of the gears 2 and 3 are arranged side plates 18 and 19 which serve to seal tooth spaces of the gears 2 and 3.
The bearing bushings 10 to 13 are arranged in the corresponding holes 6 to 9 in a manner to inwardly project at one end thereof from the cover 4 and mounting flange 5 and the projecting ends are fitted in recesses 18a and 19a respectively formed at the side plates 18 and 19 as shown in detail in FIG. 3. Between the inner ends of the bearing bushings 10 to 13 and bottoms of the recesses 18a and 19a are defined annular gaps 20 to 23, respectively, which are communicated through annular passages 18b and 19b formed at the side plates 18 and 19 to side surfaces of the gears 2 and 3 to form lubrication passageways.
The lubrication passageways are symmetrically formed. The following description will be made in connection with the passageways defined on a side of the mounting flange 5.
On an outer surface of the side plate 18 is superposedly arranged an isolation plate 24 as shown in FIG. 2. The isolation plate 24 is formed into a shape corresponding to a low pressure area L on the outer surface of the side plate 18. Reference numeral 25 designates a seal fittedly arranged so as to extend from a circumference of each of the bearing bushings 10 and 11 to a level difference portion between the isolation plate 24 and the side plate 18. The seal 25 serves to define a high pressure area H on the outer surface side of the side plate 18, in addition to the above-described low pressure area L. Low pressure formed on a side of a suction port 26 acts on the low pressure area L, whereas high pressure formed on a side of a discharge port 27 acts on the high pressure area H.
Also, the side plate 18 is formed on an inner surface thereof contacted with the gears 2 and 3 with a pair of introduction ports 18c and 18d for introducing low pressure oil therethrough, through which the suction port 26 and the above-described annular passage 18b are communicated to each other. Low pressure oil introduced through the ports 18c and 18d flows through the annular passage 18b to the annular gaps 20 and 21.
The bearing bushings 10 and 11 are formed with oil grooves 28 and 29 which extend in axial directions thereof, respectively. The oil grooves 28 and 29 serve to communicate end chambers 30 and 31 with the body section 1 in a manner to be contiguous or adjacent to outer ends of the gears 14 and 15 to the annular gaps 20 and 21 therethrough, respectively.
The end chambers 30 and 31 so communicated to the low pressure oil introducing ports 18c and 18d are communicated through return passages 32 and 33 and communication passages 34 and 35 to the suction port 26, respectively. The return passages 32 and 33 are formed using grooves formed on inner surfaces of the bushing insertion holes 6 and 7 so as to extend in axial directions thereof, respectively. More particularly, the bearing bushings 10 and 11 are pressedly inserted in the insertion holes 6 and 7 formed with the grooves to close one side of each of the grooves, resulting in the return passages 32 and 33. Accordingly, the return passages 32 and 33 may be formed using a die, for example by, aluminum die casting.
The communication passages 34 and 35 are formed by closing, with the isolation plate 24, recesses formed on an inner surface of the mounting flange 5 contacted with the isolation plate 24 during die casting.
Low pressure oil introduced through the suction port 26 into the low pressure introduction ports 18c and 18d is then circulated through the annular passage 18b , annular gaps 20 and 21, oil grooves 28 and 29, end chambers 30 and 31 of the gear shafts 14 and 15, return passages 32 and 33 and communication passages 34 and 35 while exhibiting its lubrication function and cooling the gear shafts.
As can be seen from the foregoing, in the conventional gear pump constructed as described above, a positional relationship between an inlet of the circulation passageway for lubricating oil and its outlet is limitedly specified. Accordingly, it has a disadvantage of failing to vary its rotational direction as desired.